Various efforts have hitherto been made to increase the functionality of polymeric compounds. For example, in one approach currently used to increase the refractive index of polymeric compounds, aromatic rings, halogen atoms or sulfur atoms are introduced onto the compound. Of such compounds, episulfide polymeric compounds and thiourethane polymeric compounds, both of which have sulfur atoms introduced thereon, are in practical use today as high-refractive index lenses for eyeglasses.
However, given that material design to a refractive index above 1.7 is difficult with a polymer alone, the most effective method for achieving an even higher refractive index is known to involve the use of inorganic metal oxides.
For example, a method for increasing the refractive index by using a hybrid material composed of a siloxane polymer mixed with a material containing small dispersed particles of zirconia, titania or the like has been disclosed (Patent Document 1).
A method in which a condensed ring skeleton having a high refractive index is introduced onto portions of a siloxane polymer has also been disclosed (Patent Document 2).
In addition, numerous attempts have been made to impart heat resistance to polymeric compounds. Specifically, it is well known that the heat resistance of polymeric compounds can be improved by introducing aromatic rings. For example, polyarylene copolymers with substituted arylene recurring units on the backbone have been disclosed (Patent Document 3). Such polymeric compounds show promise primarily in use as heat-resistant plastics.
Melamine resins are familiar as triazine resins, but have a very low decomposition temperature compared with heat-resistant materials such as graphite.
The heat-resistant organic materials composed of carbon and nitrogen that have been in use up until now are for the most part aromatic polyimides and aromatic polyamides. However, because these materials have straight-chain structures, their heat-resistance temperatures have not been all that high.
Triazine-based condensation materials have also been reported as nitrogen-containing polymeric materials having heat resistance (Patent Document 4).
In recent years, there has arisen a need for high-performance polymeric materials in the development of electronic devices such as liquid-crystal displays, organic electroluminescent (EL) displays, optical semiconductor (LED) devices, solid-state image sensors, organic thin-film solar cells, dye-sensitized solar cells and organic thin-film transistors (TFT).
The specific properties desired in such polymeric materials include (1) heat resistance, (2) transparency, (3) high refractive index, (4) high solubility, and (5) low volume shrinkage.
However, because the high refractive index lens materials for eyeglasses mentioned above generally have a poor heat resistance, requiring that production be carried out in a temperature range no higher than 200° C., materials of this type are unsuitable for processes such as baking in open air at 300° C.
Moreover, because polymeric compounds in which aromatic rings or triazine rings have been introduced generally have an inadequate solubility in solvents, they are insoluble in resist solvents which are safe solvents. On the other hand, materials which exhibit a high solubility generally have a low transparency.
In materials that use inorganic metal oxides, there is a trade-off between refractive index and transparency, which makes it difficult to increase the transparency while retaining a high refractive index.
Moreover, given that this material contains fine particles of differing characteristics, in the course of a dry process such as etching or ashing, the etch rate becomes unstable, making a film of uniform thickness difficult to obtain, and also resulting in a narrower process margin during device fabrication.
Highly branched polymers are broadly divided into hyperbranched polymers and dendrimers.
As used herein, “hyperbranched polymer” refers to a highly branched polymer with an irregular branched structure that is obtained by, for example, polymerizing ABx-type polyfunctional monomers (where A and B represent functional groups that react with each other, and “x” on B is a number equal to 2 or more).
“Dendrimer” refers to a highly branched polymer which has a regular branched structure. Hyperbranched polymers are characterized by being easier to synthesize than dendrimers, and by the ease with which high-molecular-weight bodies can be synthesized.
It has been reported that triazine ring-containing hyperbranched polymers have been synthesized for flame retardant applications (Non-Patent Document 1).